1. Field of the Invention
The present invention relates to a method and apparatus for detecting linear patterns.
2. Background Art
One of the greatest challenges in increasing productivity of LSI manufacturing is to improve yields. To improve yields, it is important to analyze yield loss, identify processes and manufacturing apparatuses which have been causing the yield loss at an early stage, and make improvements. However, an LSI chip is produced through hundreds of processes using hundreds of manufacturing apparatuses. Thus, once a defective LSI chip is detected, it is generally a very difficult task to identify the cause.
To deal with this, when a process is finished, defect inspection is carried out to check whether the process has been performed properly. The defect inspection is carried out optically and/or by an electron-beam technique to check a circuit pattern for any abnormality or foreign matter. The abnormality or foreign matter detected in this way is referred to as a defect. When a defect is detected, coordinates of the defect on a wafer are recorded. Defects displayed on a wafer map using recorded coordinate information are referred to as a defect map.
Defect distributions on defect maps are broadly divided into two types. One of the types involves random defects which are distributed evenly irrespective of locations on the wafer. The other type involves clustered defects which are distributed unevenly.
It has been pointed out that defects attributable to a specific process or manufacturing apparatus leave a “fingerprint” as a defect distribution on the defect map. That is, any defective condition of a process or manufacturing apparatus shows up as clustered defects unique to the process or manufacturing apparatus. Thus, classification of clustered defects provides a clue to causes of the defects.
Typical clustered defects include a linear pattern. Defects of a linear pattern are placed along a line or arc. Thanks to their characteristic shape, linear patterns, when detected, often enable identifying the process or manufacturing apparatus causing reduced yields.
Microscopically, linear patterns are divided into three types. Microscopically, the linear pattern of the first type has defects placed at small intervals without scattering. Macroscopically, the linear pattern of the first type is a sharp, clear linear pattern. Microscopically, the linear pattern of the second type has defects placed at slightly wide intervals, being scattered to some extent. Macroscopically, the linear pattern of the second type is not much different from the linear pattern of the first type. Microscopically, the linear pattern of the third type has defects placed at wide intervals. Macroscopically, the linear pattern of the third type is a faint linear pattern.
Conventional methods for detecting linear patterns include, for example, a method which uses Hough transform (Japanese Patent Laid-Open No. 2003-59984). However, the conventional method cannot detect the linear pattern of the first type and the linear pattern of the second type by making a distinction between them. Also, it is difficult for the conventional method to detect the linear pattern of the second type and the linear pattern of the third type. Furthermore, the conventional method cannot detect any of the linear patterns if the linear pattern is buried in random defects of high density.
Also, conventionally, when skipped measurements are taken in defect inspection, since the linear pattern is divided in the middle, it is not possible to detect the linear pattern. Skipped measurements are taken when defect inspection is conducted on only part of semiconductor chips on a wafer surface to reduce inspection time.